Tubular ice makers normally freeze water flowing through a length of tubing by circulating cold refrigerant through an annular space outside the tubing. As water freezes inside the tubing, an annular shaped ice mass is formed, having an outside diameter equal to the inside diameter of the tubing and having an inner diameter dependent upon the length of the freezing cycle. As the ice mass forms, the water flow through the tubing decreases in proportion to the shrinking inner diameter of the annular frozen mass, squared. Water exiting from the tubing during the freezing cycle is normally collected in a control pan or container having a small orifice in the bottom thereof for drainage. When the water flow through the tubing decreases to the point that drainage through the control pan orifice exceeds the flow into the pan, the water level inside the control pan will drop. Detection of the fall in water level thus provides a convenient means of ascertaining the end point of the freezing cycle since the control pan orifice size may be altered to produce an annular ice mass having the desired inner diameter.
After the properly sized ice is formed, hot discharge refrigerant gas from the refrigerant compressor is routed by means of a solenoid operated valve directly to the annular space outside the tubing instead of first passing the gas through the condensor and expansion valve as in the freezing cycle. The flow of hot gas replacing the cold refrigerant serves to melt the outside surface of the ice adhering to the tubing and the water pressure at the tubing inlet flushes the ice product from the tubing outlet. After the ice is thus harvested the freezing cycle may again commence.
As is readily observed, the efficiency of the system is highly dependent upon minimizing the length of the harvest cycle in comparison to the length of the freezing cycle. Care must be taken, however, to insure that all ice is removed during the harvest cycle to prevent damage to the equipment during the freezing cycle. Many problems have been encountered heretofore as a result of incomplete harvesting permitting ice blockage during the freezing cycle with subsequent rupture of the water tubing.